The Labour leader Ed Miliband had fired the "starting gun" for the next general election after his widely acclaimed speech to the party's annual conference, his deputy Harriet Harman told delegates on Thursday.

She also gave the first insight into the party's strategy, revealing that shadow cabinet ministers would pair with candidates in marginal seats to help them campaign.

In the deputy leader's traditional closing conference speech in Manchester, Harman built on the apparent success of the week and in particular Miliband's keynote speech on Tuesday in which he spelt out his vision of "one nation" Labour and "one nation" Britain.

Harman said Labour now had a "fighting chance" of ousting the Conservative-Liberal Democrat coalition in the 2015 election.

In the campaign, shadow chancellor Ed Balls will be paired with Clair Hawkins in Dover and Deal in Kent; shadow business secretary Chuka Umunna with Clive Lewis and Jessica Asato in Norwich; and Harman herself with Andrew Pakes in Milton Keynes.

"To win the next general election we must – all of us – adopt a marginal seat mindset and listen to the people where we don't have Labour MPs as well as where we do," added Harman.

"We've got to be the voice speaking up for the young couple in Dartford, as well as the young couple in Darlington," she said, echoing the ubiquitous one nation theme. "We've got to speak up for the pensioner in Gloucester, as well as Grimsby. The commuter in Milton Keynes as well as in Manchester."

Harman also appeared to have sanction to break with the unwritten rule of the week: that Labour leaders focus on attacking Tories rather than Lib Dems, in case they need to form a coalition after 2015.

Harman attacked the Lib Dems for undermining their own policy achievements, such as a higher income tax threshold and the pupil premium for children from disadvantaged backgrounds, by voting for policies to cut tax credits for the worst off and cut education spending overall.

She also attacked the Lib Dem leader Nick Clegg in person, and even Vince Cable, widely see as Clegg's replacement if the coalition party does not recover in the polls in the next year.

"Safe Vince is in it up to his neck too," said Harman, reminding delegates that it was Cable who was in charge of the big increase in university tuition fees. "I have a message for Vince: don't bother texting Ed, he's changed his number."

The first polls since Miliband's speech, published on Thursday, showed the Labour leader and the party had gained a notable bounce. A YouGov state of the parties poll gave Labour a 14 point lead over the Conservatives, up six points since Wednesday, and the Daily Mirror reported an opinion poll showing the proportion of people who see Miliband as "statesmanlike" nearly doubled from 18% to 34%.